use std::io::*;

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let n: usize = itr.next().unwrap().parse().unwrap();


    let mut a: Vec<i64> = vec![0; n];
    let mut b: Vec<i64> = vec![0; n];
    
    for i in 0..n - 1 {
        a[i] = itr.next().unwrap().parse().unwrap();
        b[i] = itr.next().unwrap().parse().unwrap();
    }

    let mut suma = 0;
    let mut sumb = 0;
    // 
    // 自分以外の所に行かなくてはいけないから、自分以外の所の和 >= 自分
    for i in 0..n - 1 {
        suma += a[i];
        sumb += b[i];
    }
    
    let mut amn = 1 << 30;
    let mut bmn = 1 << 30;
    for i in 0..n - 1 {
        // b[i] <= suma - a[i] + a_1; // が必要
        // a_1 >= b[i] - (suma - a[i])
        if b[i] >= suma - a[i] {
            amn = std::cmp::min(amn, b[i] - (suma - a[i]));
        }
        // a[i] <= sumb - b[i] + b_1;
        // b_1 >= a[i] - (suma - a[i])
        if a[i] >= sumb - b[i] {
            bmn = std::cmp::min(bmn, a[i] - (sumb - b[i]));
        }
    }
    if bmn == 1 << 30 {
        bmn = 0;
    }
    if amn == 1 << 30 {
        amn = 0;
    }

    // ここまでで、suma == sumbにしたい && a_1 <= sumb && b_1 <= suma
    // amn <= a_1 <= sumb, bmn <= b_1 <= suma

    println!("{}", std::cmp::min(sumb - amn, suma - bmn) + 1);
}